.box{
    width: 100%;
    height: 100%;
}
.top{
    width: 100%;
    height: 80px;
}
.main{
    width: 100%;
    height: calc(100% - 80px);
}
.nav{
    width: 200px;
    height: 100%;
    float: left;
}
.content{
    width: calc(100% - 200px);
    height: 100%;
    float: left;
}
.secondMenu{
    display: none;
}
